Continuously operating screenless screw-type centrifuge



F. MAURER 3,424,375

IIJOUSIJY OPERATING SCREENLESS SCREW-TYPE CENTRIFUGE Jan. 28, 1969 Z of2 Sheet Filed Oct. 9, 1957 I/vl E/ rvR FRITZ H/HARER United StatesPatent U.S. Cl. 23320 Int. Cl. B04b 9/10, 11/00 7 Claims ABSTRACT OF THEDISCLOSURE A continuously operating screenless screw-type centrifuge forremoving solids from liquid and including a centrifuge drum and ascrew-type conveyor coaxially mounted in a housing at a fixed distanceapart, the difference in speed of the drum and the screen being variablein predetermined time intervals.

BACKGROUND OF THE INVENTION Field of the invention The present inventionrelates to a continuously operating screenless screw-type centrifuge,and, more particularly, to such a centrifuge for removing abrasivesolids from cooling liquids.

Prior Art In order to remove finely divided solids or larger solidparticles from a vehicle liquid, screw-type centrifuges are generallyused. These centrifuges consist essentially of a drum and of a dischargescrew arranged within the drum. The drum has predominantly the shape ofa hollow conical frustrum within which the discharge screw is arrangedwith a slight distance being provided between the screw threads and theinner wall of the drums.

Under the action of the centrifugal force, the solidscontaining vehicleliquid forms within the drum a hollow cylinder and the solids, clue totheir higher specific gravity, are accelerated against the inner wall ofthe drum by the action of the centrifugal force. The discharge of thesesolid particles is then effected in the direction towards one end of thedrum by the relative movement of the discharge screw with respect to thedrum.

The distance of the screw threads from the inner wall of the drum and,in particular, the value of the difference in speed of rotation betweendrum and screw must be adjusted in accordance with the nature, particlesize, and quantity of the solids to be removed from the vehicle liquid.

In order to obtain the generally relatively small difference in speedbetween the outer drum and inner screw, various devices have alreadybeen proposed. For instance, it is known to drive the centrifuge drumand the discharge screw via a planetary gearing in which one of the twodrive shafts extends in the other shaft, which is hollow. Planetarygearings, however, represent extremely cumbersome and expensiveconstructions which considerably increase the overall cost of such aninstallation.

Thus it has also been proposed to produce the difference in speedbetween the discharge screw and the centrifugal drum by arranging thedischarge screw in free-wheeling manner in a directly driven drumrotating with constant speed and being braked by electrical means, suchas an eddy-current brake, or the like.

A similar braking by means of a hydrostatic transmission during thecentrifuging has also already been pro- "ice posed. The importance ofthis concept lies in the fact that the difference in speed of the drumand the discharge screw can be adapted to the nature of the materialbeing centri fuged during operation. This, however, is only of interestand importance when, aside from the best possible separation of thesolid components from the vehicle liquid, the solid component must havea predetermined density of consistency.

Further problems exist in the separation of solids from cooling liquidsfor industrial machining, since the solids consist practicallyexclusively of metal chips, grinding wheel emery, lapping pastes andgrinding dust which must be removed from the circuit of the colingliquid so as to make the latter suitable again for cooling and toprevent a clogging of the liquid conduits and damage to them. Also, ithas been found that emery and lapping paste exert an extremely abrasiveand destructive action on the inner wall of the drum so that, withoutcounter-measures, the wearing down of the screw threads of the dischargescrew and of the drum is so great after a relatively short period ofoperation, that replacement is necessary.

In order to solve this latter problem, a screw-type centrifuge has beenproposed in which a coupling is arranged between a gearing and thedischarge screw and which can be engaged and disengaged during thecentrifuging. This coupling is preferably in the form of anelectromagnetic clutch which is engaged and disengaged by means of atime-switch.

In this latter arrangement, however, the drive of the discharge screw iseffected by a friction drive which is maintained by the solidsdepositing on the inner wall of the centrifuge drum between thecentrifuge drum and the discharge worm. The operating properties,including the acceleration of the discharge screw, are thereforedependent on the nature of the solids to be separated, as well as on thethickness of the layer in which the solids particles deposit on thecentrifuge drum. In addition to this, a driving of the discharge screwonly commences upon the placing in operation of the centrifuge when,after a certain period of time, solids have already deposited on theinner wall of the centrifuge drum, so that the required frictionalengagement with the discharge screw has been brought about. Thisoperational behavior is extremely unsatisfactory, especially whenabrasive solid particles are encountered, as discussed above.

SUMMARY OF THE INVENTION A screw-type centrifuge particularly forseparating abrasive solid particles from cooling liquids for themachining industry in which the centrifuge drum and the discharge screware coupled directly with the drive device, and the differential speedbetween the two rotating elements is periodically varied automaticallybetween zero and a given predetermined difference in speeds.

The centrifuge drum and the discharge screw are connected with eachother via a freewheel and have a common drive which can be brakedperiodically during operation.

The periodic braking may be achieved by controlled reversal of phase ofan electric drive motor, the control being effected by a timing relay,or by a mechanical brake acting directly on the drive.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be explained infurther detail below with reference to the accompanying drawings inwhich:

FIGURE 1 is a longitudinal section through a screwtype centrifuge inaccordance with the invention;

r, FIGURE 2 is a cross-section along the line IIII of FIGURE 1; and

FIGURE 3 is a cross-section along the line III-III of FIGURE 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring specifically to thedrawings, the reference numeral 1 refers to a centrifuge housing 1,within which a centrifuge drum 2 is arranged for rotation about avertical axis. The centrifuge drum 2 has approximately the shape of anupward widening conical frustrum with an attached cylindrical portion.The upper wall of the centrifuge housing 1 bears a stationary hollow hub3 which extends vertically downwardly into the inside of the centrifugedrum 2 and has bearings 4 and 5 supporting drum 2. Within the hollow hub3 there extends a main drive shaft 8 which is supported in the upperhousing wall at 6 and in the drum at 7, and is fixed to a dischargescrew 9 to rotate same within the centrifuge drum 2.

Between the discharge screw 9 and the centrifuge drum 2 there isprovided a unidirectional freewheel coupling 10 so that the two rotatingelements, namely, the centrifuge drum 2 and the discharge screw 9 can bedriven jointly in the same direction by an electric motor 11 via atoothed belt 12.

The discharge screw 9 has, toward its bottom, a funnel-shaped extension13 the inside of which has runner blades 14 in the manner of a flowpump.

The centrifuge housing 1 is arranged directly over a tank 15 into whichthe cooling liquid from which the solids are to be removed continuouslyflow so that a liquid level designated 16 is continuously maintained.The funnel-shaped extension 13 of the discharge screw extends into theliquid level 16 so that, upon rotation of the discharge screw 9, theliquid is conveyed into the centrifuge drum 2 by the runner blades 14.

As shown in FIGURE 2, the screw threads of the discharge screw 9 areborne by a spider 17 between the arms of which the cooling liquid,conveyed by the funnelshaped extension 13, is passed into the inside ofthe drum.

The operation of the centrifuge is as follows. By starting the electricmotor 11, the main drive shaft 8 and the discharge screw 9 are placed inrotation via the toothed belt 12, while at the same time the centrifugedrum 2 is placed in rotation in the same direction via theunidirectional freewheel coupling 10. In this way, liquid is conveyedout of the tank 15 by the runner blades 14 into the inside of the drumas shown by the upwardly extending arrows in FIGURE 1, wherein thesolids of the cooling liquid deposit on the inner wall of the centrifugedrum 2 as a result of the centrifugal force and their greater specificgravity. The cleaned cooling liquid itself is forced through bore holes18 in the drum into an upward separating chamber 19 of the centrifugedrum 2 from which it is withdrawn under pressure.

A change in phase is now effected on the electric motor 11 which isperiodically controlled by a timing relay 20 and which causes a periodicdelaying or braking of the rotation of main drive shaft 8, and thereforedischarge screw 9. Since the centrifuge drum 2 is connected with thedrive via the freewheel coupling 10 only in one direction of rotation itis not affected by this delay in rotation, but rather rotates withpractically constant speed due to its inertia. Therefore, the rotationof discharge screw 9 periodically lags behind the centrifuge drum 2, andas a result of this periodically varied difference in speed, the solidswhich have deposited on the inner wall of the centrifuge drum 2 areconveyed by means of the relative movement of the discharge screw withrespect to the centrifuge drum 2 in the direction towards the dischargeend of smaller diameter of the latter, from which they are thrown outthrough edge grooves 21 as shown by the downwardly extending arrows inFIGURE 1. The

dry to sludge-like solids then fall through a shaft located within thetank 15 into a drawer 22 which can be emptied at certain time intervals.

The switching times of the timing relay 20 can be lengthened orshortened, depending on the degree of solids in the liquid, so that thedischarge screw 9 accordingly shows a difference in speed of rotationfrom the rotating centrifuge drum 2 only during the corresponding timeintervals.

In principle, it is immaterial which of the two rotating elementsrotates with constant speed and which with periodically variable speed.Advisedly, however, the drum will always be allowed to rotate withconstant speed, since, in view of its larger mass, a greater force wouldhave to be exerted on the drive device to slow it down.

As can be noted from FIGURE 3, spring-loaded cone valves 23 are arrangedin the drum wall of the centrifuge drum 2 both below and in theseparating chamber 19. At the operating speed, the valve bodies 24 ofthese valves are pressed against their valve seat by the centrifugalforce, so that the cone valves 23 are closed during operation. However,in order to prevent the liquid present in the space of the drum fromflowing back downward into the drawer 22 upon the shutting off of thecentrifuge, the strength of the valve springs 25 is so designed that atabout /a the operating speed the spring force of the valve springs 25pushes the valve bodies 24 inwardly against the action of the centrifugeforce and the cone valves 23 are thereby opened. In this way, thecleaned liquid present within the drum gushes under high pressurethrough the valve opening so that, upon the final stopping of thecentrifuge, the inner spaces of the drum are free of liquid. Due to theintensive flow through these valves, a depositing of solids and aclogging of the valves is prevented.

Of course several variations in the structure and arrangement of theabove are possible within the scope of the invention. For example, adevice may be provided which controls the braking frequency of the maindrive shaft as a function of the quantity of solids removed or to beremoved in such a manner that the frequency increases with an increaseof the solids in the cooling liquid.

I claim:

1. A continuously operating screw-type centrifuge for separating solidsfrom a liquid, comprising a drive shaft rotatably mounted in saidhousing, means to drive said drive shaft in a predetermined direction, ahousing, a tank disposed below said housing to initially receive saidliquid, a centrifuge drum mounted for rotation within said housing, adischarge screw mounted for rotation within said housing and extendingwithin said drum in a spaced relationship thereto, said discharge screwbeing fixed to said drive shaft for rotation therewith and extendinginto said tank for delivering the contents thereof into said housing forseparation to solids and liquids, freewheel means operatively connectingsaid drum and said drive shaft during rotation of said drive shaft insaid predetermined direction, and braking means for periodically brakingsaid drive shaft during operation so that the speed of rotation of thesaid discharge screw lags at periodic time intervals behind the speed ofrotation of the said drum.

2. The centrifuge according to claim 1, wherein said freewheel means isin the form of a unidirectional coupling member.

3. The centrifuge according to claim 1 wherein said freewheel means ismounted on said discharge screw.

4. The centrifuge according to claim 1, wherein said braking means is inthe form of a periodically controlled mechanical braking device actingon said drive means.

5. The centrifuge according to claim 1, wherein said discharge screwincludes a lower funnel-shaped cylindrically terminating extensionextending into the liquid in said tank.

6. The centrifuge according to claim 1, further comprising at least onespring-loaded cone valve provided in the wall of said drum and adaptedto be closed under the action of a predetermined centrifugal forceduring operation and to open automatically at a given speed of rotationbelow the operating speed.

7. The centrifuge according to claim 1 wherein said drive means is inthe form of an electric motor; and wherein said braking means includesmeans for selectively reversing the phase of the electric motor, and atiming relay for controlling the frequency of reversal of said phase.

References Cited UNITED STATES PATENTS ROBERT W. JENKINS, PrimaryExaminer.

US. Cl. X.R.

